Worldwide. In temperate and sub-tropical regions, and also in the tropics at higher elevations. It is recorded from Australia, New Zealand, and the highlands of Papua New Guinea.
Members of the cabbage (brassica) family, e.g., broccoli, Brussels sprout, cabbage, cauliflower. Weeds in the brassica family can be hosts.
A major disease of brassicas, caused by a fungus; it is common in areas of intensive production, with overlapping crops. It can be especially severe when wet weather occurs for 1-2 weeks, in temperatures of 16-20°C. Ringspot disease is most important on Brussels spout, cabbage, and cauliflower.
The fungus causes light brown to grey spots surrounded by a yellow halo (Photo 1). The spots are often limited by the veins and are angular, up to 20 mm across. Characteristically, tiny black fruiting bodies containing large numbers of spores, develop in concentric circles in the centre of the spots (Photo 2). These give the disease its "ringspot" name.
The spots occur on seedlings, but are more often seen on mature plants, on older leaves. If there are many spots they join together, the leaves turn yellow and die early. Spots also occur on the buds of Brussels sprout.
Spread of the fungus occurs when the fruiting bodies release spores, which are spread short distance by water splash, and in wind and rain. Long-distance spread can occur in seed.
Economic damage is caused by early death of leaves, by bud infection on Brussels sprout, and spots on cabbages that penetrate through several layers of leaves in storage, and need to be removed before sale.
Look for dark spots, up to 20 mm, with light centres containing fruiting bodies, which appear as black dots. Look to see if the spots are angular because they are prevented from growing through the leaf veins - a difference between this disease and cabbage leaf spot, caused by the fungus Alternaria brassicicola (see Fact Sheet No. 133). Look to see that the fruiting bodies are in concentric circles.
A difficult disease to control, especially in areas of intensive vegetable production, because of large numbers of airborne spores where environmental conditions are cool and wet, favouring spread and infection.
If growing crops commercially, apply regular sprays of chlorothanonil, mancozeb or copper during cool moist weather. If farmers are keeping their own seed, and getting infections in the nursery, treat seed before planting with thiram, or mancozeb; alternatively, treat seed with hotwater at 50°C for 30 minutes.
AUTHOR Grahame Jackson
Information from Pest & disease fact sheet - Mycosphaerella brassicicola. HorticultureWeek. (http://www.hortweek.com/pest-disease-factsheet-mycosphaerella-brassicicola/plant-health/article/1341919); and from (and Photos 1&2) Diseases of vegetable crops in Australia (2010). Editors, Denis Persley, Tony Cooke, Susan House. CSIRO Publishing.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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